The risk of a miscarriage appears to rise along with the father's age, regardless of how old the mother is, researchers report.

Their study looked at nearly 14,000 women who were pregnant in the 1960s and 70s.

The researchers found that the risk of miscarriage was 60% greater when the father was age 40 or older than when he was 25-29 years old.

What's more, age made a difference even for men in their 30s. Miscarriage risk was about three times greater when the man was 35-39 years of age than if he were younger than 25.

These risks were all independent of the mother's age, a well-known factor in miscarriage, the researchers report in the latest issue of the journal Obstetrics & Gynecology.

The findings add to evidence showing that, like women, men have a biological clock.

Although men continually produce new sperm and can father children late in life, research shows that their fertility gradually declines starting at a relatively young age.

Also, as with women, older fathers are more likely to have children with birth defects.

One recent study found that a man's ability to have a child fades after the age of 40, similar to a woman's fertility decline after age 35.

Another confirmed that genetic abnormalities in sperm steadily become more common as men age.

Why does it happen?

Miscarriages, particularly those in the first trimester, often occur because of genetic anomalies in the foetus, which may explain the risk tied to paternal age.

The current findings strengthen the belief that people planning a family should consider not only the woman's age, but the man's as well, according to the study authors.

"As child-bearing is increasingly delayed in Western societies, this study provides important information for people who are planning their families," write the researchers, led by Dr Karine Kleinhaus, who was with the Columbia University School of Public Health in New York at the time of the study.

Back in the 60s and 70s

The findings are based on data from a large study of women in Jerusalem who were pregnant between 1964 and 1976, about 1500 of whom suffered a miscarriage.

These women were compared with the more than 12,000 study participants who delivered a baby.

Older paternal age was linked to a higher miscarriage risk, regardless of both the woman's age and a range of other factors that contribute to miscarriage, such as smoking during pregnancy and maternal diabetes.

Still, the researchers point out, despite this generally higher miscarriage rate, older paternal age may only slightly raise the risk to any one couple.